1. Field of the Invention
This invention relates to color source sheets useful in the thermographic production of color projection transparencies.
2. Description of the Prior Art
Color source sheets have been described in Newman, U.S. Pat. No. 3,147,377 and in Clark et al., U.S. Pat. No. 3,280,735. The intermediate sheets mentioned in Dybvig et al., U.S. Pat. No. 3,601,484 likewise serve as color source sheets in the color-printing process described therein. The above patents mention cellulose acetate, ethyl cellulose, polyvinyl-toluene and polystyrene as binders for the heat-volatilizable dyestuffs, and in proportions of two to three parts by weight of binder to one part of dye. Without the binder component, the dyes are difficult to uniformly apply and are easily removed by casual contact. However, in the presence of the binder, the temperature required to cause effective transfer of the dye is higher than desired, requiring operating at undesirably high temperatures. Many of the binder formulations are found to unduly adhere to the receptor sheets when heated in contact therewith; attempts to avoid sticking by incorporation of inert particulate fillers with hard resin materials have been found to permit lateral diffusion of dye at the interface, with resultant blurring of image outline.